Common mode noise suppression with restoration of common mode signal

ABSTRACT

A processing system is disclosed. The processing system includes an amplifier configured to generate a feedback signal including a spatial common mode estimate from spatial-common-mode-processed signals. The processing system further includes charge integrators configured to obtain resulting signals from capacitive sensor electrodes, the resulting signals including a spatial common mode, and generate the spatial-common-mode-processed signals by mitigating the spatial common mode in the resulting signals using the feedback signal. The processing system also includes a controller including a programmable gain amplifier capturing the spatial common mode estimate over a summing resistor of the amplifier and a demodulator configured to remove a modulation voltage from the spatial common mode estimate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. § 120 to U.S. patent application Ser. No. 16/847,886,filed on Apr. 14, 2020, which is incorporated by referenced herein inits entirety.

TECHNICAL FIELD

The described embodiments relate generally to electronic devices, andmore specifically, to suppressing noise (e.g., display noise) associatedwith touch sensor electrodes.

BACKGROUND

Input devices, including proximity sensor devices (e.g., touchpads ortouch sensor devices), are widely used in a variety of electronicsystems. A proximity sensor device may include a sensing region, oftendemarked by a surface, in which the proximity sensor device determinesthe presence, location and/or motion of one or more input objects.Proximity sensor devices may be used to provide interfaces for theelectronic system. For example, proximity sensor devices may be used asinput devices for larger computing systems (e.g., opaque touchpadsintegrated in, or peripheral to, notebook or desktop computers).Proximity sensor devices are also often used in smaller computingsystems (e.g., touch screens integrated in cellular phones). Proximitysensor devices may also be used to detect input objects (e.g., finger,styli, pens, fingerprints, etc.).

SUMMARY

In general, in one aspect, one or more embodiments relate to aprocessing system comprising: an amplifier configured to generate afeedback signal comprising a spatial common mode estimate from aplurality of spatial-common-mode-processed signals; a plurality ofcharge integrators configured to: obtain a plurality of resultingsignals from a plurality of capacitive sensor electrodes, the pluralityof resulting signals comprising a spatial common mode; and generate theplurality of spatial-common-mode-processed signals by mitigating thespatial common mode in the plurality of resulting signals using thefeedback signal; and a controller comprising: a programmable gainamplifier capturing the spatial common mode estimate over a summingresistor of the amplifier; and a demodulator configured to remove amodulation voltage from the spatial common mode estimate.

In general, in one aspect, one or more embodiments relate to a methodcomprising: generating, by an amplifier, a feedback signal comprising aspatial common mode estimate from a plurality ofspatial-common-mode-processed signals; obtaining a plurality ofresulting signals from a plurality of capacitive sensor electrodes, theplurality of resulting signals comprising a spatial common mode;generating the plurality of spatial-common-mode-processed signals bymitigating the spatial common mode in the plurality of resulting signalsusing the feedback signal; capturing, by a programmable gain amplifier,the spatial common mode estimate over a summing resistor of theamplifier; removing, by a demodulator, a modulation voltage from thespatial common mode estimate.

In general, in one aspect, one or more embodiments relate to an inputdevice comprising: a plurality of capacitive sensor electrodes; anamplifier configured to generate a feedback signal comprising a spatialcommon mode estimate from a plurality of spatial-common-mode-processedsignals; and a plurality of charge integrators configured to: obtain aplurality of resulting signals from the plurality of capacitive sensorelectrodes, the plurality of resulting signals comprising a spatialcommon mode; and generate the plurality of spatial-common-mode-processedsignals by mitigating the spatial common mode in the plurality ofresulting signals using the feedback signal; and a controllercomprising: a programmable gain amplifier capturing the spatial commonmode estimate over a summing resistor of the amplifier; and ademodulator configured to remove a modulation voltage from the spatialcommon mode estimate.

BRIEF DESCRIPTION OF DRAWINGS

The present embodiments are illustrated by way of example and are notintended to be limited by the figures of the accompanying drawings.

FIG. 1 shows a block diagram of an input device in accordance with oneor more embodiments.

FIG. 2 shows an input device with a common mode noise suppressioncircuit enabling retrieval of a common mode signal, in accordance withone or more embodiments.

FIG. 3A shows a current conveyor in accordance with one or moreembodiments.

FIG. 3B shows a sensor electrode configuration in accordance with one ormore embodiments.

FIG. 4 shows a flowchart in accordance with one or more embodiments.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature, and isnot intended to limit the disclosed technology or the application anduses of the disclosed technology. Furthermore, there is no intention tobe bound by any expressed or implied theory presented in the precedingtechnical field, background, or the following detailed description.

In the following detailed description of embodiments, numerous specificdetails are set forth in order to provide a more thorough understandingof the disclosed technology. However, it will be apparent to one ofordinary skill in the art that the disclosed technology may be practicedwithout these specific details. In other instances, well-known featureshave not been described in detail to avoid unnecessarily complicatingthe description.

Throughout the application, ordinal numbers (e.g., first, second, third,etc.) may be used as an adjective for an element (i.e., any noun in theapplication). The use of ordinal numbers is not to imply or create anyparticular ordering of the elements nor to limit any element to beingonly a single element unless expressly disclosed, such as by the use ofthe terms “before”, “after”, “single”, and other such terminology.Rather, the use of ordinal numbers is to distinguish between theelements. By way of an example, a first element is distinct from asecond element, and the first element may encompass more than oneelement and succeed (or precede) the second element in an ordering ofelements.

Various embodiments of the present disclosure provide input devices andmethods that facilitate improved detectability of input objects. Theinput device operates by using sensor electrodes that detect changes insignal. A common mode noise suppression circuit is used to mitigatenoise to which the sensor electrodes may be exposed. Various aspects ofa common mode noise suppression circuit are more fully described in U.S.patent application Ser. No. 16/373,369, the full disclosure of which isincorporated herein by reference.

One source of noise is a display screen. The sensor electrodes may beapproximately equally exposed to the noise, regardless of the locationof the sensor electrodes. Accordingly, the noise acts like a spatialcommon mode on the signals obtained from the sensor electrodes. Anotherspatial common mode may be a background signal as estimated by abaseline. The baseline may be a measurement of the signals obtained fromthe sensor electrodes when no input object is present in the sensingregion. The baseline may be approximately similar across the sensorelectrodes, regardless of the location of the sensor electrodes.Additional details regarding noise and baseline affecting the sensing bythe sensor electrodes are provided below.

The common mode noise suppression circuit may be used to mitigatespatial common modes such as the described noise and/or baseline. Thecommon mode noise suppression circuit may mitigate a spatial common moderegardless of the nature of the spatial common mode. Accordingly, thecommon mode noise suppression circuit may mitigate not only undesiredspatial common modes, but also spatial common modes that may be ofinterest. For example, the common mode noise suppression circuit mayremove or reduce the spatial common mode signal associated with a largeobject, when the large object spans all or the majority of sensingelectrodes and approximately equally affects the signals of the sensorelectrodes. As a result of the mitigation of the spatial common mode bythe common mode noise suppression circuit, the presence of the largeobject may not be detected, unless additional processing is performed.

In one or more embodiments of the disclosure, the spatial common mode ismitigated by analog circuits. One or more embodiments convert anestimate of the spatial common mode from analog domain to digital domainin order for reconstruction of the full sensor signals of the sensorelectrodes, despite the mitigation of the spatial common mode by theanalog circuits. As a result, embodiments of the disclosure providevarious benefits of the mitigation of the spatial common mode in theanalog domain, while still allowing the detection of large objects,enabled by an additional processing in the digital domain. Theimplementation of the mitigation of the spatial common mode in theanalog domain and the processing of an estimate of the spatial commonmode in the digital domain are subsequently discussed.

Turning now to the figures, FIG. 1 shows a block diagram of an exemplaryinput device (100), in accordance with embodiments of the disclosure.The input device (100) may be configured to provide input to anelectronic system (not shown for simplicity). As used in this document,the term “electronic system” (or “electronic device”) broadly refers toany system capable of electronically processing information. Examples ofelectronic systems may include personal computers of all sizes andshapes (e.g., desktop computers, laptop computers, netbook computers,tablets, web browsers, e-book readers, and personal digital assistants(PDAs)), composite input devices (e.g., physical keyboards, joysticks,and key switches), data input devices (e.g., remote controls and mice),data output devices (e.g., display screens and printers), remoteterminals, kiosks, video game machines (e.g., video game consoles,portable gaming devices, and the like), communication devices (e.g.,cellular phones, such as smart phones), and media devices (e.g.,recorders, editors, and players such as televisions, set-top boxes,music players, digital photo frames, and digital cameras). Additionally,the electronic system could be a host or a slave to the input device.

The input device (100) may be implemented as a physical part of theelectronic system. In the alternative, the input device (100) may bephysically separate from the electronic system. The input device (100)may be coupled to (and communicate with) components of the electronicsystem using various wired or wireless interconnections andcommunication technologies, such as buses and networks. Exampletechnologies may include Inter-Integrated Circuit (I2C), SerialPeripheral Interface (SPI), PS/2, Universal Serial Bus (USB),Bluetooth®, Infrared Data Association (IrDA), and various radiofrequency (RF) communication protocols defined by the IEEE 802.11 orother standards.

In the example of FIG. 1, the input device (100) may correspond to aproximity sensor device (such as a “touchpad” or a “touch sensordevice”) configured to sense input provided by one or more input objects(140) in a sensing region (120). Example input objects include fingersand styli. The sensing region (120) may encompass any space above,around, in and/or near the input device (100) in which the input device(100) is able to detect user input (e.g., provided by one or more inputobjects (140)). The sizes, shapes, and locations of particular sensingregions may vary depending on actual implementations.

In some embodiments, the sensing region (120) detects inputs involvingno physical contact with any surfaces of the input device (100). Inother embodiments, the sensing region (120) detects inputs involvingcontact with an input surface (e.g., a touch screen) of the input device(100) coupled with some amount of applied force or pressure.

The input device (100) may utilize any combination of sensor componentsand sensing technologies to detect user input in the sensing region(120). The input device (100) includes one or more sensing elements fordetecting user input. As several non-limiting examples, the input device(100) may use capacitive, resistive, and/or inductive techniques. Theinput device (100) may also include one or more physical or virtualbuttons (130) to collect user input.

In some embodiments, the input device (100) may utilize capacitivesensing technologies to detect user input. For example, the sensingregion (120) may input one or more capacitive sensing elements (e.g.,sensor electrodes) to create an electric field. The input device (100)may detect inputs based on changes in the capacitance of the sensorelectrodes. More specifically, an object in contact with (or in closeproximity to) the electric field may cause changes in the voltage and/orcurrent in the sensor electrodes. Such changes in voltage and/or currentmay be detected as “signals” indicative of user input. The sensorelectrodes may be arranged in arrays or other regular or irregularpatterns of capacitive sensing elements to create electric fields. Insome implementations, some sensing elements may be ohmically shortedtogether to form larger sensor electrodes. Some capacitive sensingtechnologies may utilize resistive sheets that provide a uniform layerof resistance.

Some capacitive sensing technologies may be based on “self capacitance”(also referred to as “absolute capacitance”) and/or mutual capacitance(also referred to as “trans-capacitance”). Absolute capacitance sensingmethods detect changes in the capacitive coupling between sensorelectrodes and an input object. Trans-capacitance sensing methods detectchanges in the capacitive coupling between sensor electrodes. Forexample, an input object near the sensor electrodes may alter theelectric field between the sensor electrodes, thus changing the measuredcapacitive coupling of the sensor electrodes. In some embodiments, theinput device (100) may implement trans-capacitance sensing by detectingthe capacitive coupling between one or more transmitter sensorelectrodes (also “transmitter electrodes” or “transmitter”) and one ormore receiver sensor electrodes (also “receiver electrodes” or“receiver”). The resulting signal received by a receiver electrode maybe affected by environmental interference (e.g., other electromagneticsignals) as well as input objects in contact with, or in close proximityto, the sensor electrodes.

The processing system (110) may be configured to operate the hardware ofthe input device (100) to detect input in the sensing region (120). Theprocessing system (110) may include parts of, or all of, one or moreintegrated circuits (ICs) and/or other circuitry components. In someembodiments, the processing system (110) also includeselectronically-readable instructions, such as firmware code, softwarecode, and/or the like. In some embodiments, components composing theprocessing system (110) are located together, such as near sensingelement(s) of the input device (100). In other embodiments, componentsof processing system (110) are physically separate with one or morecomponents close to the sensing element(s) of the input device (100),and one or more components elsewhere. For example, the input device(100) may be a peripheral coupled to a computing device, and theprocessing system (110) may include software configured to run on acentral processing unit of the computing device and one or more ICs(perhaps with associated firmware) separate from the central processingunit. As another example, the input device (100) may be physicallyintegrated in a mobile device, and the processing system (110) mayinclude circuits and firmware that are part of a main processor of themobile device. In some embodiments, the processing system (110) isdedicated to implementing the input device (100). In other embodiments,the processing system (110) also performs other functions, such asoperating display screens, driving haptic actuators, etc. For example,the processing system (110) may be part of an integrated touch anddisplay controller.

In some embodiments, the processing system (110) may includedetermination circuitry (150) configured to determine when at least oneinput object is in a sensing region, determine signal to noise ratio,determine positional information of an input object, identify a gesture,determine an action to perform based on the gesture, a combination ofgestures or other information, and/or perform other operations. In someembodiments, the processing system (110) may include sensor circuitry(160) configured to drive the sensing elements to transmit transmittersignals and receive the resulting signals. In some embodiments, thesensor circuitry (160) may include sensory circuitry that is coupled tothe sensing elements. The sensory circuitry may include, for example, atransmitter module including transmitter circuitry that is coupled to atransmitting portion of the sensing elements and a receiver moduleincluding receiver circuitry coupled to a receiving portion of thesensing elements.

Although FIG. 1 shows only determination circuitry (150) and sensorcircuitry (160), alternative or additional circuitry may exist inaccordance with one or more embodiments of the disclosure.

In some embodiments, the processing system (110) responds to user input(or lack of user input) in the sensing region (120) directly by causingone or more actions. Example actions include changing operation modes,as well as graphical user interface (GUI) actions such as cursormovement, selection, menu navigation, and other functions. In someembodiments, the processing system (110) provides information about theinput (or lack of input) to some part of the electronic system (e.g., toa central processing system of the electronic system that is separatefrom the processing system (110), if such a separate central processingsystem exists). In some embodiments, some part of the electronic systemprocesses information received from the processing system (110) to acton user input, such as to facilitate a full range of actions, includingmode changing actions and GUI actions.

For example, in some embodiments, the processing system (110) operatesthe sensing element(s) of the input device (100) to produce electricalsignals indicative of input (or lack of input) in the sensing region(120). The processing system (110) may perform any appropriate amount ofprocessing on the electrical signals in producing the informationprovided to the electronic system. For example, the processing system(110) may digitize analog electrical signals obtained from the sensorelectrodes. As another example, the processing system (110) may performfiltering or other signal conditioning. As yet another example, theprocessing system (110) may subtract or otherwise account for abaseline, such that the information reflects a difference between theelectrical signals and the baseline. A baseline is an estimate of theraw measurements of the sensing region when an input object is notpresent. For example, a capacitive baseline is an estimate of thebackground capacitance of the sensing region. Each sensing element mayhave a corresponding individual value in the baseline. As yet furtherexamples, the processing system (110) may determine positionalinformation, recognize inputs as commands, recognize handwriting, andthe like.

In some embodiments, the input device (100) includes a touch screeninterface, and the sensing region (120) overlaps at least part of anactive area of a display screen (155). The input device (100) mayinclude substantially transparent sensor electrodes overlaying thedisplay screen (155) and provide a touch screen interface for theassociated electronic system. The display screen may be any type ofdynamic display capable of displaying a visual interface to a user, andmay include any type of light emitting diode (LED), organic LED (OLED),cathode ray tube (CRT), liquid crystal display (LCD), plasma,electroluminescence (EL), or other display technology. The input device(100) and the display screen may share physical elements. For example,some embodiments may utilize some of the same electrical components fordisplaying and sensing. In various embodiments, one or more displayelectrodes of a display device may be configured for both displayupdating and input sensing. As another example, the display screen (155)may be operated in part or in total by the processing system (110).

The sensing region (120) and the display screen (155) may be integratedand follow on-cell or in-cell or hybrid architectures. In other words,display screen (155) may be composed of multiple layers (e.g., one ormore polarizer layers, color filter layers, color filter glass layers,thin film transistor (TFT) circuit layers, liquid crystal materiallayers, TFT glass layers, etc.). The sensor electrodes may be disposedon one or more of the layers. For example, the sensor electrodes may bedisposed on the TFT glass layer and/or the color filter glass layer.Moreover, the processing system (110) may be part of an integrated touchand display controller that operates both the display functions and thetouch sensing functions.

Although not shown in FIG. 1, the processing system, the input device,and/or the host system may include one or more computer processor(s),associated memory (e.g., random access memory (RAM), cache memory, flashmemory, etc.), one or more storage device(s) (e.g., a hard disk, anoptical drive such as a compact disk (CD) drive or digital versatiledisk (DVD) drive, a flash memory stick, etc.), and numerous otherelements and functionalities. The computer processor(s) may be anintegrated circuit for processing instructions. For example, thecomputer processor(s) may be one or more cores or micro-cores of aprocessor. Further, one or more elements of one or more embodiments maybe located at a remote location and connected to the other elements overa network. Further, embodiments may be implemented on a distributedsystem having several nodes, where each portion of the disclosure may belocated on a different node within the distributed system. In oneembodiment, the node corresponds to a distinct computing device.Alternatively, the node may correspond to a computer processor withassociated physical memory. The node may alternatively correspond to acomputer processor or micro-core of a computer processor with sharedmemory and/or resources.

While FIG. 1 shows a configuration of components, other configurationsmay be used without departing from the scope of the disclosure. Forexample, various components may be combined to create a singlecomponent. As another example, the functionality performed by a singlecomponent may be performed by two or more components.

FIG. 2 shows an input device (200) in accordance with one or moreembodiments. The input device (200) may correspond to input device(100), discussed above in reference to FIG. 1. Various elementsintroduced in FIG. 2 may correspond to elements shown in FIG. 1. Forexample, FIG. 2 introduces sensor electrodes which may be associatedwith the sensing region (120) of FIG. 1. FIG. 2 also introduces elementsconfigured to drive and to sense the sensor electrodes. These elementsmay correspond to the sensor module (160) of FIG. 1. FIG. 2 furtherintroduces elements that are associated with evaluating signals obtainedfrom the sensor electrodes. These elements may correspond to thedetermination module (150). As shown in FIG. 2, the input device (200)includes multiple touch sensor electrodes (e.g., sensor electrode 1(205A)-sensor electrode N (205N)), multiple charge integrators (chargeintegrator 1 (210A)-charge integrator N (210N)), an amplifier (240), anda controller (280). The output of the amplifier (240) is coupled to thecharge integrators (210A-210N) by a feedback loop (278).

The multiple sensor electrodes (205A-205N) may be used to perform anytype of capacitive sensing (e.g., absolute capacitance sensing,trans-capacitance sensing, etc.). The sensor electrodes (205A-205N) maybe driven by a modulation voltage V_(MOD), and the output of each sensorelectrode (205A-205N) is a resulting signal (e.g., resulting signal1-resulting signal N) which reflects the presence of an input object, ifany, proximate to the capacitive sensor electrode (205A-205N).

In one or more embodiments, input device (200) includes a noise source(207). The noise source (207) may correspond to any common mode noise(Vn). For example, the noise source (207) may generate noise (Vn) duringthe operation of a display screen (e.g., display screen (155), discussedabove in reference to FIG. 1). Accordingly, the noise source (207) maybe a display noise source. The noise source (207) may correspond, forexample, to a cathode layer of an LED screen and/or a common electrode(VCOM) in an LCD screen. As shown in FIG. 2, the noise source (207)couples to the touch sensor electrodes (205A-205N). In other words, theresulting signal (e.g., resulting signal 1-resulting signal N) from eachsensor electrode (205A—205N) may include some component of the noise(Vn) of the noise source (207). In one or more embodiments, the couplingbetween the display noise source (207) and each sensor electrode(205A-205N) may be modeled as impedance Z_(B). For example, Z_(B) may bea resistor (R_(B)) and a capacitor (C_(B)) in series:Z_(B)=R_(B)+1/(sC_(B)).

In one or more embodiments, the noise (Vn) affects the sensor electrodes1-N (205A-205N) in a similar manner. Accordingly, the resulting signals1-N may include a spatial common mode, reflecting the noise (Vn). Thecommon mode is spatial because it may be present on the resultingsignals 1-N regardless of the spatial location of the correspondingsensor electrodes (205A-205N). For example, assume that the sensorelectrodes (205A-205N) are distributed over the surface of a screen(e.g., an LED or LCD screen). In this example, the spatial common modeis a result of the same or similar Vn coupling into the resultingsignals 1-N of the sensing electrodes (205A-205N). Similarly, a spatialcommon mode may be present when a large object (299) covers the sensingelectrodes (205A-205N), because the resulting signals 1-N may besimilarly biased due to the presence of the large object in proximity tothe sensor electrodes (205A-205N). In one or more embodiments, the largeobject covers a substantial fraction of the sensor electrodes, or allsensor electrodes. The large object may be, for example, a palm restingon a touch surface, a face in proximity to a sensing region used forfacial recognition, etc. In case of the spatial common mode being causedby the noise (Vn), the spatial common mode may include an alternatingcurrent (AC) component with a frequency of the noise (Vn). In case ofthe spatial common mode being caused by a large object, the spatialcommon mode may include a direct current (DC) component.

As discussed above, the input device (200) includes multiple chargeintegrators (210A-210N). There may be one charge integrator for each ofthe sensor electrodes (205A-205N). Moreover, each charge integrator andits corresponding sensor electrode may form, at least in part, achannel. As shown in FIG. 2, each charge integrator (210A-210N) inputsboth a resulting signal from the corresponding sensor electrode(205A-205N) and a feedback signal (275) from the output of the amplifier(240). The feedback signal (275) propagates along the feedback loop(278). Further, each charge integrator may be implemented as anoperational amplifier in parallel with a switch and a feedback impedanceZ_(FB) (e.g., Z_(FB)=1/(sC_(FB))). C_(B) may be much larger than C_(FB)(C_(B)>>C_(FB)), and thus Z_(FB) is much larger than Z_(B)(Z_(FB)>>Z_(B)). The output of each charge integrator (210A-210N) is aspatial-common-mode-processed signal (e.g.,spatial-common-mode-processed signal 1-spatial-common-mode-processedsignal N). As shown in FIG. 2, the spatial-common-mode-processed signalsare inputs to both the controller (280) and the amplifier (240). In oneor more embodiments, in the spatial-common-mode-processed signals 1-N,the spatial common mode is mitigated, i.e., reduced, partiallyeliminated, almost entirely or entirely eliminated, in comparison to thecorresponding resulting signals 1-N. A discussion of the mitigation ofthe common mode, performed by the input device (200), is provided below.

As discussed above, the input device (200) includes an amplifier (240).The amplifier (240) may amplify (e.g., scale) eachspatial-common-mode-processed signal (i.e.,spatial-common-mode-processed signal 1-spatial-common-mode-processedsignal N) by a factor of −A/N, where N is the number (i.e., cardinality)of spatial-common-mode-processed signals (i.e., number of channels), andwhere A is a gain value. As shown in FIG. 2, the amplifier (240) may beimplemented with multiple input resistors (R_(IN)) and multiple currentconveyors (current conveyor 1 (220A)-current conveyor N (220N)).Specifically, there may be one input resistor (R_(IN)) and one currentconveyor (220A-220N) per spatial-common-mode-processed signal (i.e., perchannel). The amplifier (240) may also include a buffer (255) storingvalue V_(MOD), and a summing resistor (260) with a resistance ofA×R_(IN)×(1/N). The mitigation of the spatial common mode by the variouscircuit elements is described below.

In one or more embodiments, the input device (200) includes thecontroller (280). The controller (280) is configured to determine, basedon the output of one or more charge integrators (210A-210N), theposition of an input object(s), if any, in a sensing region defined bythe sensor electrode (205A-205N) (e.g., sensing region (120), discussedabove in reference to FIG. 1). The controller (280) may be implementedin hardware (i.e., circuits), software, or any combination thereof. Thecontroller (280) may correspond to either a touch controller thatoperates the touch sensing functions or an integrated touch and displaycontroller that operates both the display functions and the touchsensing functions.

In FIG. 2, some element of the controller (280) are shown. Morespecifically, the controller (280) includes a demodulator (282A) and ananalog-to-digital converter (284A) outputting a digital touch signal(286A) for sensor electrode 1 (205A). The digital touch signal (286A) isobtained based on the spatial-common-mode-processed signal 1, andtherefore does not include the common mode of the resulting signal 1, oronly a fraction of the common mode, depending on the effectiveness ofthe mitigation of the spatial common mode. The controller (280) furtherincludes a demodulator (282N) and an analog-to-digital converter (284N)outputting a digital touch signal (286N) for sensor electrode N (205N).The digital touch signal (286N) is obtained based on thespatial-common-mode-processed signal N, and therefore does not includethe common mode of the resulting signal N, or only a fraction of thecommon mode, depending on the effectiveness of the mitigation of thespatial common mode.

The controller (280) may include one demodulator and oneanalog-to-digital converter for each of the sensor electrodes of theinput device (200). The controller (280) also includes a programmablegain amplifier (PGA) (290), a demodulator (292), and ananalog-to-digital converter (296) outputting a digital spatial commonmode estimate (298). The digital spatial common mode estimate (298) isobtained by analog-to-digital converting the spatial common modeestimate (294). The spatial common mode estimate (294) is obtained fromthe voltage VRs over the summing resistor (260), measured by the PGA(290), and processed by the demodulator (292). The demodulators(282A-282N, 292) may include a mixer and a low pass filter. The mixermay perform a multiplication operation, e.g., using V_(MOD), prior to alow-pass filtering operation by the low-pass filter. The operation ofthe controller (280) is described below with reference to the flowchartof FIG. 4.

The digital touch signals (286A-286N) and/or the digital spatial commonmode estimate (298) may subsequently be digitally processed by acomputer processor. Processing steps may include the detection ofobjects of various sizes, e.g., small objects, large objects, etc. Inone or more embodiments, the detection of large objects involves theprocess of the digital touch signals (286A-286N) and the digital spatialcommon mode estimate (298) in combination, as discussed below withreference to the flowchart of FIG. 4.

In one or more embodiments, the amplifier (240) and the feedback loop(278), when coupled to the charge integrators (210A-210N), form a commonmode noise suppression circuit The common mode noise suppression circuitincludes the spatial common mode estimate (294) in the feedback signal(275), enabling the subtraction of the spatial common mode estimate(294) from the resulting signals 1-N to mitigate the spatial common modeon the resulting signals 1-N. Consider, for example, noise emitted bythe noise source, Vn (207), and picked up by the sensor electrodes(205A-205N). Without the common mode noise suppression circuit, thenoise gain (ci_(VOUT)/Vn) is: ci_(VOUT)/Vn=Z_(FB)/Z_(B). SinceZ_(FB)>>Z_(B), the noise gain is larger than one. Accordingly, withoutthe common mode noise suppression circuit, the controller (280)processes a potentially very noisy signal, which could lead to incorrectoutput results (e.g., detecting an input object when no input object ispresent, determining the wrong location of an input object, etc.).However, when the common mode noise suppression circuit is present, thenoise gain (ci_(VOUT)/Vn) may be determined as:ci_(VOUT)/Vn=−(Z_(FB)/Z_(B))×1/(A+1+AZ_(FB)/Z_(B)). In many embodiments,A is much larger than 1 (i.e., A>>1), and the noise gain may beapproximated as: ci_(VOUT)/Vn=(−1/A)×(Z_(FB)/Z_(B))×1/(1+Z_(FB)/Z_(B)).Substituting Z_(B)=R_(B)+1/(sC_(B)) and Z_(FB)=1/(sC_(FB)),ci_(VOUT)/Vn=(−1/A)×C_(B)×1/(C_(B)+C_(FB))×1/(1+sR_(B)C_(FB)∥C_(B))).

In other words, with the common mode noise suppression circuit, thenoise (Vn) may be mitigated by 1/A×1/(1+Z_(FB)/Z_(B)) before processingby the controller (280). Since Z_(FB)>>Z_(B), the attenuation may beapproximated as 1/A×Z_(B)/Z_(FB). Other common mode noise including thecommon mode component of global coarse baseline cancellation (GCBC),and/or a spatial common mode introduced by the presence of the largeobject (299) may also be attenuated by the common mode noise suppressioncircuit. As the touch sensor processor (280) is processing a less noisysignal, it is less likely that the output results of the touch sensorprocessor will be incorrect.

In one or more embodiments, with the common mode noise suppressioncircuit, the signal transfer function for the channel proximate to aninput object (ci_(VOUT1)) may be approximated as:ci_(VOUT1)=dC_(B)(1−1/N)V_(MOD), where dC_(B) is the change incapacitance between the display noise source (207) and the sensorelectrode due to the input object, and V_(MOD) is the modulation voltagein the buffer (255). The signal transfer functions for the remainingchannels ci_(VOUTX, X≠1) (i.e., the channels not proximate to the inputobject) may be approximated as: ci_(VOUTX, X≠1)=(−1/N)×dC_(B)×V_(MOD).In other words, the touched sensor pixel (i.e., tixel) shows almost fullresponse and untouched tixels show a small response in the opposedirection.

The above description is in the context of absolute capacitance (orself-capacitance) sensing. The described circuit also applies totrans-capacitance (or mutual capacitance) sensing. In trans-capacitancesensing, V_(MOD) is typically held at a constant voltage (e.g. VDD/2), atransmitter with voltage swing Vtx drives trans-capacitance, andproximity is detected by measuring a change in C_(t), or dC_(t). Thesuppression of noise Vn follows the same equation:ci_(VOUT)/Vn=(−1/A)×C_(B)×1/(C_(B)+C_(FB))×1/(1+sR_(B)C_(FB)∥C_(B))).The signal transfer function for a touch tixel isci_(VOUT1)=−dC_(t)(1−1/N)V_(tx), and ci_(VOUTX, X≠1)=1/N×dC_(t)×V_(tx)for untouched tixels.

FIG. 3A shows a current conveyor (300) in accordance with one or moreembodiments. The current conveyor (300) may correspond to any of thecurrent conveyors (220A-220N) discussed above in reference to FIG. 2. Asshown in FIG. 3A, the current conveyor (300) may include an operationalamplifier (305) and one or more current mirrors (310) coupled to anoutput of the operational amplifier (305). Those skilled in the art,having the benefit of this detailed description, will appreciate thatthe input current to the current conveyor (300) and the output currentfrom the current conveyor (300) may be identical or substantiallyidentical in magnitude, but opposite in direction.

In one or more embodiments, the common mode noise suppression circuitincludes 4 poles: the dominant pole in the operational amplifier of acharge integrator, the pole at ci_(VOUT), the pole at i_(IN) of thecurrent conveyor (300), and the pole at ci_(VREF) (shown in FIG. 2). Inone or more embodiments, in order to stabilize the loop, a stabilizationimpedance (315) including resistor R_(Z) and a capacitor C_(Z) is addedas shown in FIG. 3A. This creates a pole and a zero in the currentconveyor. The pole is typically dominant with A>>1, which narrow bandsthe loop. The zero gives a phase boost to get enough phase margin. Thoseskilled in the art, having the benefit of this detailed description,will appreciate that there are other ways to stabilize the loop withoutusing R_(Z) and C_(Z). For example, stabilizing the loop may be achievedby increasing the compensation capacitor in the charge integrator, whicheffectively moves the dominant pole to a lower frequency.

FIG. 3B shows a sensor electrode configuration in accordance with one ormore embodiments. The sensor electrode configuration (350) is for anabsolute capacitance sensing and is intended to illustrate how a sensingby a sensor electrode may be affected by the presence of an objectand/or noise. The sensor electrode configuration uses resistive andcapacitive elements to model the absolute capacitance sensing. Inparticular, dC_(B) (354), a capacitance to an object (e.g., the largeobject (299)) may contribute to the sensing signal. dC_(B) (354), in oneor more embodiments, is the capacitance that ultimately enables theinput device to determine whether an object is present in the sensingregion, or not. Further, C_(B) (352), a background capacitance to astructural component, e.g., a cathode layer of an LED screen and/or acommon electrode (VCOM) in an LCD screen) may contribute to the sensingsignal. The contribution may include an AC component such as Vn (207),e.g., noise (Vn) emitted by the LED or LCD screen.

FIG. 4 shows a flowchart in accordance with one or more embodiments. Theflowchart of FIG. 4 depicts a method for operating an input device(e.g., input device (200)). One or more of the steps in FIG. 4 may beperformed by the components of the input device (200), discussed abovein reference to FIG. 2 and/or the input device (100), discussed abovewith reference to FIG. 1. In one or more embodiments, one or more of thesteps shown in FIG. 4 may be omitted, repeated, and/or performed in adifferent order than the order shown in FIG. 4. Accordingly, the scopeof the disclosure should not be considered limited to the specificarrangement of steps shown in FIG. 4.

In one or more embodiments, the subsequently described method is for acommon mode noise suppression allowing a restoration of a common modesignal. The common mode noise suppression is based on analog circuitelements that form a common mode noise suppression circuit, e.g., asshown in FIG. 2. As previously described, the common mode noisesuppression circuit may mitigate a spatial common mode regardless of thenature of the spatial common mode. For example, the common mode noisesuppression circuit may remove noise, but also the signal associatedwith a large object.

Removing the spatial common mode by analog circuits may have benefits.For example, the subtraction of the spatial common mode estimate fromthe resulting signals may prevent a saturation of the chargeintegrators, thereby avoiding signal clipping. The mitigation of thespatial common mode may thus enable the use of smaller feedbackcapacitors at the charge integrators while still avoiding saturation.Further, since a capacitive baseline of the sensor electrodes may besimilar across the sensor electrodes, the capacitive baseline may beeffectively eliminated or reduced by the mitigation of the spatialcommon mode, without requiring a dedicated baseline correction.

Despite these advantages, it may be desirable to obtain the entiresignals (the resulting signals, in FIG. 2) associated with the sensorelectrodes, including the spatial common mode, or at least a componentof the spatial common mode. In one or more embodiments, the subsequentlydescribed method enables a digital restoration of the spatial commonmode after an analog-to-digital conversion. The restored spatial commonmode may subsequently be used for various purposes. For example, therestored spatial common mode may be used to detect large objects, asdescribed below. Further, the restored spatial common mode may be usedto determine a capacitive baseline of the sensor electrodes.

Briefly summarized, the following method may thus provide a spatialcommon mode mitigation by analog circuits, followed by a restoration ofthe spatial common mode by digital processing.

Initially, in Step 400, baselining is performed to get a zero signaloutput at ci_(VOUT). In other words, ci_(VOUT) is measured without touchand without amplifier feedback (i.e., A=0), but with V_(MOD) active.Under such conditions, the measured ci_(VOUT) reflects the fixedcapacitance in the sensor. A coarse baseline cancellation (CBC) circuit(not shown) may or may not be used to remove the fixed capacitance inthe sensor so net changes in capacitance can be more easily detected. Inone or more embodiments, following execution of Step 400, the inputdevice is ready for interaction (e.g., touch sensing) with a user.Execution of Step 400 is optional.

In Step 405, a feedback signal is generated. The feedback signal isgenerated by amplifying spatial-common-mode-processed signals based on again value and a cardinality of the spatial-common-mode-processedsignals (i.e., the number of spatial-common-mode-processed signals). Thegain between the output of each charge integrator and the output of theloop (i.e., ci_(VREF)) is (−g_(m)R_(s))×1/(1+g_(m)R_(IN)), where R_(s)is the resistance of the summing resistor (260). For g_(m)R_(IN)>>1,this gain may be approximated as −R_(s)/R_(IN). For N channels with acommon mode noise signal, the gain becomes −N×R_(s)/R_(IN). By settingR_(s)=A×R_(IN)×(1/N), the gain becomes −A for N channels or −A/N foreach channel, where N is the cardinality of thespatial-common-mode-processed signals (i.e., the cardinality of thechannels). Accordingly, the feedback signal may be understood asincluding a spatial common mode estimate. Based on the describedcircuitry, the spatial common mode estimate is or approximates anaverage over the resulting signals 1-N. The amplifier may be implementedwith multiple current conveyors and a single summing resistor. Thefeedback signal is the output of the amplifier.

In Step 410, one or more resulting signals are obtained. The resultingsignals are associated with sensor electrodes involved in any type ofcapacitive sensing. There may be coupling between the sensor electrodesand a noise source (e.g., a display noise source). Accordingly, theresulting signals may include a component associated with the noisesource, and the resulting signals may further reflect the presence of aninput object, if any, proximate the sensor electrodes. In one or moreembodiments, the resulting signals include a spatial common mode. Thespatial common mode may be associated with, for example, noise and/or alarge object.

In Step 415, the spatial-common-mode-processed signals are generated bymitigating the spatial common mode in the resulting signals using thefeedback signal. The spatial common mode may be mitigated regardless ofthe nature of the spatial common mode. For example, a spatial commonmode resulting from noise may be mitigated, and/or a spatial common moderesulting from a large object may be mitigated. The mitigation mayinvolve the resulting signals and the feedback signal as inputs to thecharge integrators. Each charge integrator may integrate a differencebetween one of the resulting signals and the feedback signal. Becausethe feedback signal, in one or more embodiments, includes the spatialcommon mode estimate, the spatial common mode is mitigated. The outputof a charge integrator is a spatial-common-mode-processed signal. Thefeedback loop, the amplifier, and the charge integrators effectively actas a common mode noise suppression circuit.

Steps 400-415 are performed in the analog domain. Accordingly, whileSteps 400-415 have been separately described, Steps 400-415 may besimultaneously performed by an analog circuit such as the analog circuitdescribed with reference to FIG. 2.

In Step 420, digital touch signals are obtained from thespatial-common-mode-processed signals. A demodulation followed by ananalog-to-digital conversion may be performed to obtain the digitaltouch signals. The demodulation may be performed using a multiplicationoperation, e.g., using V_(MOD), followed by a low-pass filteringoperation, thereby removing the modulation voltage V_(MOD). Thoseskilled in the art will appreciate that different demodulation methodsmay be used, without departing from the disclosure. Step 420 may beperformed for one or more digital touch signals, for example, for allsensor electrodes.

In Step 425, a digital spatial common mode estimate is obtained from thespatial common mode estimate. A demodulation followed by ananalog-to-digital conversion may be performed to obtain the digitalspatial common mode estimates. The demodulation may be performed using amultiplication operation, e.g., using V_(MOD), followed by a low-passfiltering operation thereby removing the modulation voltage V_(MOD).Those skilled in the art will appreciate that different demodulationmethods may be used, without departing from the disclosure.

In Step 430, one or more digital resulting signals may be obtained bycombining one or more of the digital touch signals with the digitalspatial common mode estimate. For example, a digital touch signal may beadditively combined with the digital spatial common mode estimate. Adigital resulting signal may, thus, approximate the resulting signalinitially obtained from the corresponding sensor electrode. For example,if the resulting signal is affected by a spatial common mode, thedigital resulting signal may also include the spatial common mode, or acomponent of the spatial common mode.

In one or more embodiments, the digital spatial common mode and/or thedigital resulting signals are further processed, e.g., by filtering.Specifically, low-pass filtering may be applied to eliminate orattenuate high-frequency components while passing low-frequency and/orDC components. The filtering may be performed in the analog domain,e.g., by the low-pass filters of the demodulators, by an additionalanalog filter, and/or by a filter in the digital domain. The digitalresulting signal, thus, may include a component of the spatial commonmode carrying information about the presence of a large object, but maynot include a component of the spatial common mode associated withnoise.

Consider, for example, the scenario illustrated in FIG. 2. In theexample, the spatial common mode includes a component associated withthe presence of a large object, and further includes a componentassociated with noise. In the example, after the low-pass filtering, thedigital resulting signal may include the component associated with thepresence of the large object (substantially a DC signal that passes thelow-pass filter), but not the component associated with the noise(substantially a high-frequency AC signal that is attenuated by thelow-pass filter). Step 430 may be performed for a single digital touchsignal, for multiple digital touch signals, or for all digital touchsignals associated with the sensor electrodes of the input device.

In Step 435, the one or more digital resulting signals are used toperform a detection task. The detection task may be, for example, anobject detection and/or a baseline detection task.

The detection of a large object may be performed based on an evaluationof the digital resulting signals across the sensor electrodes of theinput device. In comparison to an evaluation of the digital resultingsignal at an earlier point in time (in absence of the large object), thedigital resulting signals differ, indicating the presence of the largeobject. While the digital touch signals alone (without the digitalspatial common mode estimate) may not provide any indication of thepresence of the large object, as a result of the common mode mitigation,the explicit consideration of the digital spatial common mode estimatein the digital resulting signals enables the detection of the largeobject. The detection may not be adversely affected by noise, becauselow-pass filtering may have attenuated the noise. Accordingly, anerroneous detection (e.g., the detection of an object when no object ispresent, the detection of an object in the wrong position, etc.) is lesslikely.

The following sensing scenarios briefly illustrate the operations in theanalog and digital domains resulting in certain outcomes in presence ofsmall objects and large objects. Those skilled in the art willappreciate that the sensing scenarios are merely intended to serve asexamples. The disclosure is not limited to these use cases.

-   (1) In absence of a large object, the digital spatial common mode    estimate corresponds to a sampled and filtered G×Vn, with G being    the gain of the programmable gain amplifier. This corresponds to the    spatial common mode associated with the noise injected by the noise    source, in FIG. 2. The digital spatial common mode estimate may be    applied to any of the digital touch signals to restore a full    signal, as sensed by the corresponding sensor electrode(s). In other    words, a digital resulting signal reflecting the resulting signal of    the corresponding sensor electrode may be obtained for any sensor    electrode, in absence of the large object. Depending on, for    example, how low-pass filtering is performed, this digital resulting    signal may or may not include the noise Vn. The sensing scenario may    apply to a complete absence of objects in the sensing region, and to    a presence of one or more small objects, e.g. input objects, in the    sensing region. An input object may be detected based on one or more    of the digital touch signals, without necessarily requiring    consideration of the digital spatial common mode. For example, an    input object may be detected based on a change of one or more of the    digital touch signals, and/or based on a difference of a digital    touch signal of a sensor electrode to another digital touch signal    of an adjacently located sensor electrode.-   (2) In presence of a large object, the digital spatial common mode    estimate corresponds to: G×(Vn+dC_(B)/C_(B)×V_(MOD))×G_(demod_filt),    with G being the gain of the programmable gain amplifier, and    G_(demod_filt) being the gain of the demodulator and filter. The    filter gain is frequency-dependent: With the demodulation being    performed synchronously to V_(MOD), and the filter operating at the    frequency of V_(MOD), G_(demod_filt)=1 for the signal    G×dC_(B)/C_(B)×V_(MOD), while G×Vn is attenuated by the filter. As a    result, the digital spatial common mode estimate does not depend on    the display noise, while still enabling the evaluation of a common    mode capacitance associated with the large object, e.g., a face near    an input surface. Such information may be used, for example, to turn    off the display, when a face is detected in proximity to the    display.

Thus, the embodiments and examples set forth herein were presented inorder to best explain various embodiments and their particularapplication(s) and to thereby enable those skilled in the art to makeand use the embodiments. However, those skilled in the art willrecognize that the foregoing description and examples have beenpresented for the purposes of illustration and example only. Thedescription as set forth is not intended to be exhaustive or to belimiting to the precise form disclosed.

While many embodiments have been described, those skilled in the art,having benefit of this disclosure, will appreciate that otherembodiments can be devised which do not depart from the scope.

What is claimed is:
 1. A processing system comprising: an amplifierconfigured to generate a feedback signal comprising a spatial commonmode estimate from a plurality of spatial-common-mode-processed signals;a plurality of charge integrators configured to: obtain a plurality ofresulting signals from a plurality of capacitive sensor electrodes, theplurality of resulting signals comprising a spatial common mode, andgenerate the plurality of spatial-common-mode-processed signals bymitigating the spatial common mode in the plurality of resulting signalsusing the feedback signal; and a controller comprising: a programmablegain amplifier capturing the spatial common mode estimate over a summingresistor of the amplifier, and a demodulator configured to remove amodulation voltage from the spatial common mode estimate.
 2. Theprocessing system of claim 1, wherein the demodulator comprises alow-pass filter configured to attenuate a high-frequency component ofthe spatial common mode estimate.
 3. The processing system of claim 2,wherein the low-pass filter is configured to attenuate noise associatedwith a display.
 4. The processing system of claim 1, wherein thecontroller is configured to: obtain at least one resulting signal bycombining at least one of the plurality of spatial-common-mode-processedsignals with the spatial common mode estimate, and determine that alarge object is proximate to the plurality of capacitive sensorelectrodes based on the at least one resulting signal differing from theat least one resulting signal obtained in absence of the large object.5. The processing system of claim 4, wherein the spatial common modecomprises a component associated with the large object proximate to theplurality of capacitive sensor electrodes.
 6. The processing system ofclaim 1, wherein the controller is configured to: obtain at least oneresulting signal by combining at least one of the plurality ofspatial-common-mode-processed signals with the spatial common modeestimate, and determine that an input object is proximate to at leastone of the plurality of capacitive sensor electrodes based on the atleast one resulting signal.
 7. The processing system of claim 1, whereinthe spatial common mode comprises a component associated with a baselineof the plurality of capacitive sensor electrodes.
 8. The processingsystem of claim 1, wherein the amplifier comprises: a plurality of inputresistors coupled to the plurality of charge integrators; a plurality ofcurrent conveyors coupled to the plurality of input resistors; and thesumming resistor coupled to the plurality of current conveyors.
 9. Theprocessing system of claim 8, wherein: each of the plurality of inputresistors comprises a resistance of R; the gain value is A; thecardinality of the plurality of spatial-common-mode-processed signals isN; the summing resistor comprises a resistance of A×R×(1/N); and theamplifier amplifies each of the plurality ofspatial-common-mode-processed signals by −A/N.
 10. The processing systemof claim 8, wherein each of the plurality of current conveyorscomprises: an operational amplifier; a plurality of current mirrorscoupled to an output of the operational amplifier; and a stabilizationimpedance coupled to an input of the operational amplifier.
 11. Theprocessing system of claim 1, wherein: each of the plurality of chargeintegrators comprises an operational amplifier in parallel with animpedance; and the feedback signal is coupled to a non-inverting inputof each of the plurality of charge integrators.
 12. A method comprising:generating, by an amplifier, a feedback signal comprising a spatialcommon mode estimate from a plurality of spatial-common-mode-processedsignals; obtaining a plurality of resulting signals from a plurality ofcapacitive sensor electrodes, the plurality of resulting signalscomprising a spatial common mode; generating the plurality ofspatial-common-mode-processed signals by mitigating the spatial commonmode in the plurality of resulting signals using the feedback signal;capturing, by a programmable gain amplifier, the spatial common modeestimate over a summing resistor of the amplifier; and removing, by ademodulator, a modulation voltage from the spatial common mode estimate.13. The method of claim 12, further comprising: attenuating ahigh-frequency component of the spatial common mode estimate by alow-pass filter of the demodulator.
 14. The method of claim 13, whereinthe attenuated high-frequency component is noise associated with adisplay.
 15. The method of claim 12, further comprising: obtaining atleast one resulting signal by combining at least one of the plurality ofspatial-common-mode-processed signals with the spatial common modeestimate, and determining that a large object is proximate to theplurality of capacitive sensor electrodes based on the at least oneresulting signal differing from the at least one resulting signalobtained in absence of the large object.
 16. The method of claim 15,wherein the spatial common mode comprises a component associated withthe large object proximate to the plurality of capacitive sensorelectrodes.
 17. An input device comprising: a plurality of capacitivesensor electrodes; an amplifier configured to generate a feedback signalcomprising a spatial common mode estimate from a plurality ofspatial-common-mode-processed signals; and a plurality of chargeintegrators configured to: obtain a plurality of resulting signals fromthe plurality of capacitive sensor electrodes, the plurality ofresulting signals comprising a spatial common mode, and generate theplurality of spatial-common-mode-processed signals by mitigating thespatial common mode in the plurality of resulting signals using thefeedback signal; and a controller comprising: a programmable gainamplifier capturing the spatial common mode estimate over a summingresistor of the amplifier, and a demodulator configured to remove amodulation voltage from the spatial common mode estimate.
 18. The inputdevice of claim 17, wherein the controller is configured to: obtain atleast one resulting signal by combining at least one of the plurality ofspatial-common-mode-processed signals with the spatial common modeestimate, and determine that a large object is proximate to theplurality of capacitive sensor electrodes based on the at least oneresulting signal differing from the at least one resulting signalobtained in absence of the large object.
 19. The input device of claim17, wherein the controller is configured to: obtain at least oneresulting signal by combining at least one of the plurality ofspatial-common-mode-processed signals with the spatial common modeestimate, and determine that an input object is proximate to at leastone of the plurality of capacitive sensor electrodes based on the atleast one resulting signal.
 20. The input device of claim 17, wherein:each of the plurality of charge integrators comprises an operationalamplifier in parallel with an impedance; and the feedback signal iscoupled to a non-inverting input of each of the plurality of chargeintegrators.